The invention is directed to an improved apparatus for monitoring and controlling electronic equipment, especially in an emergency operation mode, wherein a microprocessor fails to supply a normal operation signal to operate that equipment.
In electronic equipment controlled by microprocessors, it is known to provide monitoring devices which monitor the correct functioning of the equipment and emit an alarm signal and/or furnish an emergency control in the event of a malfunction.
It is known in this respect to generate control pulses in a regular time sequence which serve as an indication that the equipment is functioning properly. In equipment controlled by microprocessors, these control pulses may for instance be generated by incorporating such control pulses in the control program of the microprocessor, so that in the event of program malfunctions (for instance, a shutdown of the calculator), no further control pulses are emitted.
A reset circuit for a microcomputer is known from German Offenlegungsschrift No. DE-OS 30 35 896, in which the control pulses indirectly effect the charging or discharging of a capacitor, so that the absence of control pulses can be recognized by monitoring the capacitor voltage. Then in the event that control pulses are absent beyond a predetermined extent, a reset signal is generated, which resets the microcomputer; the reset phase is followed immediately by an active or clearance phase in which the system is capable of starting up again.
The known devices have the disadvantage, however, that if a malfunction occurs either the monitored device is shut down completely or, if a reset and clearance phase is provided, then the prevailing operating conditions may be indefinite.